I like collecting on dry spells (no rain for days at a time) at little-used boat ramps on an incoming tide above 1/2 tide (3 hours into the flood tide). It helps your chance of getting the cleanest non-diluted water. Ramps or beaches on the ocean, not in harbors or marshes are better. Nahant Town dock ramp is quiet, and on the ocean. Can back right down and fill, just beware it drops off a few feet at the end on low tide, so once you fall off, you are OFF!!! It is algae covered at low tide too, slippery! Town sticker only needed if parking, go at night and be silent, turn off headlamps while loading and the neighbors won’t call PD on you. Nahanters are known for harassing outsiders. I grew up nearby and went to college in Nahant, but have not been in years. Great spot to collect NSW though. Cool fish show around the pier at night too! Bonus of collecting here at night is the ton of amphipods and other zooplankton attracted to the dock lights. If you wanted some as feed/herbivores to add to your tank this was a go to spot. You could just scoop them with a regular aquarium net at times.